1. Field of the Invention
The present invention relates to a method of making a diffraction grating device in which an optical waveguide is irradiated, by way of a phase grating, with light capable of inducing a refractive index modulation in an optical waveguide region of the optical waveguide so as to form a diffraction grating in the optical waveguide region; the diffraction grating device made by this method; and an apparatus for making the same.
2. Related Background Art
Diffraction grating device has diffraction grating formed in optical waveguide region of optical waveguide (encompassing both optical fiber and planar optical waveguide) and is used as optical filter and the like. Such a diffraction grating device is manufactured as follows. Namely, by way of a phase grating, an optical waveguide is irradiated with a predetermined wavelength of light capable of inducing a refractive index modulation (which is ultraviolet light in general, and will hereinafter be referred to as xe2x80x9crefractive index modulation inducing lightxe2x80x9d). Then, interference fringes of the refractive index modulation inducing light are generated in an optical waveguide region of the optical waveguide. Hence, the refractive index at a predetermined part of the optical waveguide region provided with the interference fringes is modulated, whereby a diffraction grating is formed.
Here, laser light emitted from a light source such as a KrF laser light source, which outputs the refractive index modulation inducing light, has a luminous flux diameter smaller than the length of the diffraction grating to be manufactured. As a consequence, a diffraction grating having a desirable length is made when the refractive index modulation inducing light is made incident on the phase grating while being scanned in a longitudinal direction of the optical waveguide.
The inventors have studied the conventional technique mentioned above and, as a result, have found a problem as follows. Namely, when making a diffraction grating, e.g., when making a uniform diffraction grating, a phase grating having a uniform diffraction efficiency distribution within a plane should be used. However, since the diffraction efficiency distribution of phase grating is not always set uniformly within a plane, a nonuniform diffraction grating may be made even if a uniform diffraction grating is intended to be made. Thus, the above-mentioned conventional technique has been problematic in that diffraction grating having desirable characteristics cannot be made if the diffraction efficiency distribution of a phase grating deviates from its desirable distribution.
For overcoming the above-mentioned problem, it is an object of the present invention to provide a method of making a diffraction grating device which can make a diffraction grating having a desirable characteristic even when the diffraction efficiency distribution of phase grating deviates from a desirable distribution, the diffraction grating device made by this method, and an apparatus for making the same.
The present invention provides a method of making a diffraction grating device, in which an optical waveguide is irradiated, by way of a phase grating, with refractive index modulation inducing light capable of inducing a refractive index modulation in an optical waveguide region of the optical waveguide so as to form a diffraction grating in the optical waveguide region; the method comprising: (1) a diffraction efficiency distribution measuring step of measuring a diffraction efficiency distribution of the phase grating; and (2) a refractive index modulating step of irradiating the optical waveguide with the refractive index modulation inducing light by way of the phase grating with an amount of irradiation of the refractive index modulation inducing light at each position on the phase grating being adjusted according to the diffraction efficiency distribution measured in the diffraction efficiency distribution measuring step, so as to modulate a refractive index of the optical waveguide region.
Preferably, in the method of making a diffraction grating device in accordance with the present invention, the diffraction efficiency distribution measuring step is carried out prior to the refractive index modulating step. Alternatively, it is preferred that the diffraction efficiency distribution measuring step be carried out simultaneously with the refractive index modulating step, and that the amount of irradiation of refractive index modulation inducing light at each position on the phase grating be feedback-controlled according to the diffraction efficiency distribution of phase grating measured in the diffraction efficiency distribution measuring step.
In the method of making a diffraction grating device in accordance with the present invention, it is preferred that the refractive index modulation inducing light be made incident on the phase grating while being scanned in a longitudinal direction of the optical waveguide in the refractive index modulating step, and that the intensity of the refractive index modulation inducing light irradiating each position on the phase grating be adjusted upon the scanning.
In the method of making a diffraction grating device in accordance with the present invention, it is preferred that the refractive index modulation inducing light be made incident on the phase grating while being scanned in a longitudinal direction of the optical waveguide in the refractive index modulating step, and that the scanning speed of the refractive index modulation inducing light irradiating each position on the phase grating be adjusted upon the scanning.
The present invention provides a diffraction grating device made by the above-mentioned method of making a diffraction grating device.
The present invention provides an apparatus for making a diffraction grating device, in which an optical waveguide is irradiated, by way of a phase grating, with refractive index modulation inducing light capable of inducing a refractive index modulation in an optical waveguide region of the optical waveguide so as to form a diffraction grating in the optical waveguide region; the apparatus comprising: (1) diffraction efficiency distribution measuring means for measuring a diffraction efficiency distribution of the phase grating; and (2) refractive index modulating means for irradiating the optical waveguide with the refractive index modulation inducing light by way of the phase grating with an amount of irradiation of the refractive index modulation inducing light at each position on the phase grating being adjusted according to the diffraction efficiency distribution measured by the diffraction efficiency distribution measuring means, so as to modulate a refractive index of the optical waveguide region.
Preferably, in the apparatus for making a diffraction grating device in accordance with the present invention, the diffraction efficiency distribution measuring means measures the diffraction efficiency distribution of the phase grating before the refractive index modulating means irradiates the phase grating with the refractive index modulation inducing light. Alternatively, it is preferred that the diffraction efficiency distribution measuring means measure the diffraction efficiency distribution of phase grating at the same time when the refractive index modulating means irradiates the phase grating with the refractive index modulation inducing light, and that the refractive index modulating means feedback-control the amount of irradiation of refractive index modulation inducing light at each position on the phase grating according to the diffraction efficiency distribution of phase grating measured by the diffraction efficiency distribution measuring means.
In the apparatus for making a diffraction grating device, the refractive index modulating means may comprise irradiating means for making the refractive index modulation inducing light incident on the phase grating while scanning the refractive index modulation inducing light in a longitudinal direction of the optical waveguide, and irradiation intensity adjusting means for adjusting the intensity of the refractive index modulation inducing light irradiating each position on the phase grating when the refractive index modulation inducing light is scanned by the irradiating means.
In the apparatus for making a diffraction grating device, the refractive index modulating means may comprise irradiating means for making the refractive index modulation inducing light incident on the phase grating while scanning the refractive index modulation inducing light in a longitudinal direction of the optical waveguide, and scanning speed adjusting means for adjusting the scanning speed of the refractive index modulation inducing light irradiating each position on the phase grating when the refractive index modulation inducing light is scanned by the irradiating means.
The present invention provides an apparatus for making a diffraction grating device, in which a diffraction grating is made in an optical waveguide region of an optical waveguide, the apparatus comprising: (1) a light source for emitting refractive index modulation inducing light capable of inducing a refractive index modulation in the optical waveguide region; (2) a phase grating for diffracting the refractive index modulation inducing light emitted from the light source; (3) a mirror for reflecting the refractive index modulation inducing light emitted from the light source so as to make the refractive index modulation inducing light incident on the phase grating; (4) a moving unit for moving the mirror along a longitudinal direction of the optical waveguide; and (5) an irradiation intensity control unit for controlling the irradiation intensity of the refractive index modulation inducing light emitted from the light source.
The present invention provides an apparatus for making a diffraction grating device, in which a diffraction grating is made in an optical waveguide region of an optical waveguide, the apparatus comprising: (1) a light source for emitting refractive index modulation inducing light capable of inducing a refractive index modulation in the optical waveguide region; (2) a phase grating for diffracting the refractive index modulation inducing light emitted from the light source; (3) a mirror for reflecting the refractive index modulation inducing light emitted from the light source so as to make the refractive index modulation inducing light incident on the phase grating; (4) a moving unit for moving the mirror along a longitudinal direction of the optical waveguide; and (5) a speed control unit for controlling, according to a diffraction efficiency distribution of the phase grating, the moving speed of the mirror moved by the moving unit.
The apparatus for making a diffraction grating device in accordance with the present invention may further comprise a light-receiving device provided so as to sandwich the phase grating between the light-receiving device and the mirror.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.